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<?php $str = '#helloworld #test #video #youtube Bon Iver are the best daily surprise :D'; preg_match_all('/#([^\s]+)/', $str, $matches); echo '<pre>'; print_r($matches); $hashtags = implode(',', $matches[1]); var_dump($hashtags);
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.24 - 5.5.35, 5.6.8 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.10, 7.2.0 - 7.2.33, 7.3.12 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
<pre>Array ( [0] => Array ( [0] => #helloworld [1] => #test [2] => #video [3] => #youtube ) [1] => Array ( [0] => helloworld [1] => test [2] => video [3] => youtube ) ) string(29) "helloworld,test,video,youtube"

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